(i) Field of the Invention:
This invention relates to a brake booster which is to vary a force magnifying ratio if necessary.
(ii) Description of Prior Art:
Prior brake boosters have a constant force magnifying ratio. Thus, when vehicle weight is varied by the movable load or the like of the vehicle and the pedalling force of a brake pedal is constant, the braking distance of the vehicle is necessarily varied under braking from the same speed of the vehicle. Hence, in the vehicle provided with the prior brake booster, the pedalling force of the brake pedal needs to be increased properly according to the movable load so as to provide a predetermined braking distance. However, considerable experiences are needed for such proper operation and the increase of the pedalling force of the brake pedal causes the fatigue of a driver.